Carbon Fiber

Successfully used in aerospace, motor sports and other applications for years, carbon fiber is also considered the ultimate material for high- performance bicycles. With an incredibly high strength-to-weight ratio, carbon fiber is an engineer’s dream. It’s lighter than aluminum and stronger than steel, and a properly constructed carbon fiber frame can produce an incredible ride quality that’s stiff, agile and efficient.

Grading Carbon Fiber

Raw carbon fiber is made with extremely thin, strong fibers. These fibers come in many different grades—or in engineering terms “modulus”— based on the material’s strength and stiffness. The higher the grade, the more it costs.

Higher grades of carbon fiber have a higher tensile modulus and are therefore stiffer. This is a good thing. However, high-grade carbon fiber can also be trickier to work with because of the need to maintain a balance between stiffness, strength and durability. It’s that balance that Felt always strives for. A frame that’s simply lighter, or stiffer, isn’t necessarily better. The goal is to balance all the elements that make a bike perform best when it hits the road or trail.

In addition to being a challenge to optimize, higher-grade carbon fiber is also more expensive. For these reasons, many bicycle manufacturers steer clear of the material. But Felt believes the investment is worthwhile. Starting with the best materials available is essential to achieving the ride quality our engineers, and our professional athletes, demand.

Making the Frames

There are many ways to use carbon fiber in bicycle manufacturing. At one end of the spectrum is an age-old method called lug-and-tube. This is the way steel-tube frames have been built for more than a century. With this method, carbon fiber tubes are bonded to lugs, which can be made from aluminum, titanium or carbon fiber. The tubes are inserted into the lugs and the joint is glued together.

The lug-and-tube technique typically uses an overlap of extra material and therefore results in a frame that’s heavier than necessary. This type of construction also produces a “flatter” ride feel because it requires many individual parts and overbuilt intersections.

At the opposite extreme is the technique used by Felt: Dynamic Monocoque Construction. We start with sheets of unidirectional fiber (picture long, straight, black hair). These sheets can be made from fibers with different levels of modulus (60T, 40T and 30T), depending on the intended usage of the bike. They can also be mixed and matched. All of Felt’s carbon fiber bikes feature a blend of materials, which is why we call them UHC, or Ultra Hybrid Carbon.

There are three levels of UHC frames: UHC Ultimate+Nano, UHC Advanced and UHC Performance. Each targets different types of riders and serves different goals. For instance, is the bike aimed at competitive racers who favor light weight and pure performance over everything else? Or is it a sprinter’s bike, built for someone who prefers additional stiffness at the cost of a few grams?

The different types of carbon fiber can also be precisely positioned in the frame to take maximum advantage of their specific properties. For example, stiffer fiber plies may be used in areas of peak stress such as the bottom bracket shell and down tube while higher-strength fiber plies are used in areas particularly susceptible to impact.

Once the perfect blend of materials is established through CAD modeling, prototype testing and athlete feedback the final recipe is documented for production—this is called the “lay-up schedule.” The lay-up schedule details the types of materials and exactly how they are assembled to produce the frame, outlining the exact order and orientation of all the individual carbon fiber sheets, or “plies,” which are assembled by hand to create the frame. These plies come “pre-impregnated” with resin, and each is meticulously cut to the shapes needed to construct the frame.

The plies get strategically laid onto specially shaped internal molds, and once that process is complete the material is placed into a symmetrically split CNC-machined mold (think waffle iron). The mold halves are then closed and locked, and the frame gets formed with a precise amount of pressure and heat.

With high-end performance bikes such as the F1, DA, Edict, or F1X, Felt takes the process a few steps further. One of Felt’s key technological manufacturing breakthroughs is a proprietary molding process called InsideOut Internally Optimized Molding. By placing specially designed molds inside the frames during this process, Felt is able to eliminate any excess material inside the carbon fiber tubing.

“These inserts really clean up the inside of the frames,” says Felt engineer Ty Buckenberger. “The bottom bracket and other junctions are all nice and clean with no excess material inside.”

Felt also employs Dynamic Monocoque Construction to form and then join the individually molded sections of its performance frames. Using this process, Felt engineers can optimize every section of the frame by molding them individually. Combining Dynamic Monocoque Construction with InsideOut Internally Optimized Molding allows Felt to have precisely sized internal molds for different tubing sizes and shapes.

“Obviously the shapes we’re working with for the front triangle are much different than those of the seatstay, for instance,” says Buckenberger. “Dynamic Monocoque Construction allows us to really focus on making every single section of the frame the best it can be.”

Finally, the frame sections are joined using a special co-molding technique. The individual sections are bonded together and then co-wrapped. Processes like InsideOut and Dynamic Monocoque Construction are considerably more complicated and expensive than other methods. But the ride quality and unparalleled strength make it worthwhile.

Felt Carbon Fiber Grades

Felt currently uses three types of its own specific blends of carbon fiber: UHC Ultimate+Nano, UHC Advanced and UHC Performance.

UHC Ultimate+Nano

The absolute finest blend of frame material in the world. With a cutting-edge construction technique and Nano resin system, UHC Ultimate+Nano frames maximize the amount of high modulus material that can be used. The secret is the proprietary resin matrix. With most carbon bicycle frames, standard epoxy resin is used as a binder to hold the individual fibers together in their desired locations and orientations. But Felt’s Nano Tech actually enhances the performance of the frame at the molecular level with a stronger bond between the individual fibers.

This system results in improved impact strength, but it also enhances the performance characteristics of the bike. How? By giving Felt engineers more options. With improved strength and impact resistance, they can use more high modulus material to add stiffness without the frame becoming too fragile. The thinner walls, improved stiffness and responsive ride quality are all results of the Nano Tech resin. Felt could have chosen to shave a few more grams off the UHC Ultimate+Nano frames, but with the bikes already below minimum competition weight, they instead increased the impact strength and stiffness. So Felt’s stiffest and lightest frame is also incredibly durable.

UHC Advanced

The highly refined threads of UHC Advanced have a higher fiber to resin ratio, which results in a lightweight, lively frame that’s perfect for competitive riders and racers. Similar to the way metal frames gain ride quality and liveliness with thinner tube walls, UHC Advanced fibers allow designers to use thin-walled tubing. The end result? UHC Advanced frames are 20% lighter while remaining just as stiff and strong.

Working with UHC Advanced fibers does present certain engineering challenges. For instance, a fiber with more stiffness and strength is also more brittle. Though capable of sustaining massive loads, these fibers are less tolerant of tight-radius bends in the manufacturing process. So thoughtful design is critical. Felt engineers are careful to include as few tight bends as possible, which not only prevents the fibers from fracturing during manufacturing but also guarantees that the material yields the lightest possible frame.

UHC Performance

Felt’s UHC Performance material clearly illustrates why carbon fiber is ideal for performance bicycle frames. Consider the facts: It’s eight times stronger than 3/2.5 titanium, more than three times stiffer than 6061 aluminum and less than one-fourth the density of steel. And it can be formed into a wide variety of shapes and exhibits nearly infinite fatigue life.

UHC Performance frames have that signature Felt feel, plus unmatched durability. They are perfect for riders who want a performance bike that’s strong enough to last for years. The UHC Performance materials used in Felt’s entry-level carbon road race bikes are on par with many manufacturers’ top-of-the-line models. There’s a reason Felt’s less expensive carbon bikes are so evolved. Just a few years ago, the same technology was used for Felt’s top-of-the-line F1 SL frameset. So today’s F5 incorporates all the advantages of a bike that, not too long ago,

was the flagship pro road racing bike. Because of Felt’s commitment to advancing its carbon fiber technology, you can experience a level of performance previously unheard of at this price.